scholarly journals Destruction of dimethyl ether and methyl formate by collisions with He+

2019 ◽  
Vol 625 ◽  
pp. A72 ◽  
Author(s):  
Daniela Ascenzi ◽  
Andrea Cernuto ◽  
Nadia Balucani ◽  
Paolo Tosi ◽  
Cecilia Ceccarelli ◽  
...  
Keyword(s):  
Dimethyl Ether ◽  
Cross Sections ◽  
Methyl Formate ◽  
Molecular Ions ◽  
Rate Coefficients ◽  
Langevin Model ◽  
Chemical Systems ◽  
Prestellar Cores ◽  
Temperature Dependences ◽  
Proton Transfer Reactions

Context. To correctly model the abundances of interstellar complex organic molecules (iCOMs) in different environments, both formation and destruction routes should be appropriately accounted for. While several scenarios have been explored for the formation of iCOMs via grain and gas-phase processes, much less work has been devoted to understanding the relevant destruction pathways, with special reference to (dissociative) charge exchange or proton transfer reactions with abundant atomic and molecular ions such as He+, H3+ and HCO+. Aims. By using a combined experimental and theoretical methodology we provide new values for the rate coefficients and branching ratios (BRs) of the reactions of He+ ions with two important iCOMs, namely dimethyl ether (DME) and methyl formate (MF). We also review the destruction routes of DME and MF by other two abundant ions, namely H3+ and HCO+. Methods. Based on our recent laboratory measurements of cross sections and BRs for the DME/MF + He+ reactions over a wide collision energy, we extended our theoretical insights on the selectivity of the microscopic dynamics to calculate the rate coefficients k(T) in the temperature range from 10 to 298 K. We implemented these new and revised kinetic data in a general model of cold and warm gas, simulating environments where DME and MF have been detected. Results. Due to stereodynamical effects present at low collision energies, the rate coefficients, BRs and temperature dependences here proposed differ substantially from those reported in KIDA and UDfA, two of the most widely used astrochemical databases. These revised rates impact the predicted abundances of DME and MF, with variations up to 40% in cold gases and physical conditions similar to those present in prestellar cores. Conclusions. This work demonstrates that the accuracy of astrochemical models can be improved by a thorough characterisation of the destruction routes of iCOMs. The details of the chemical systems can, indeed, strongly affect their efficiency and significant deviations with respect to the commonly used Langevin model estimates are possible.

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

2020 ◽  
Vol 494 (4) ◽  
pp. 5675-5681 ◽  
Author(s):  
Sanchit Chhabra ◽  
T J Dhilip Kumar
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Cross Sections ◽  
Energy Surface ◽  
Molecular Ions ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

scholarly journals Astrophysically motivated laboratory measurements of deuterium reacting with isotopologues of H

2019 ◽  
Vol 15 (S350) ◽  
pp. 114-115
Author(s):  
K. P. Bowen ◽  
P.-M. Hillenbrand ◽  
J. Liévin ◽  
X. Urbain ◽  
D. W. Savin
Keyword(s):  
Cross Sections ◽  
Zero Point ◽  
Rate Coefficients ◽  
Laboratory Measurements ◽  
Exchange Reactions ◽  
Point Energy ◽  
Chemical Tracers ◽  
Prestellar Cores ◽  
Order Of Magnitude ◽  
High Level

AbstractH2D+ and D2H+ are important chemical tracers of prestellar cores due to their pure rotational spectra that can be excited at the ~20 K temperature of these environments. The use of these molecules as probes of prestellar cores requires understanding the chemistry that forms and destroys these molecules. Of the eight key reactions that have been identified (Albertssonet al. 2013), five are thought to be well understood. The remaining three are the isotope exchange reactions of atomic D with H $${ + \over 3}$$ , H2D+, and D2H+. Semi-classical results differ from the classical Langevin calculations by an order of magnitude (Moyano et al. 2004). To resolve this discrepancy, we have carried out laboratory measurements for these three reactions. Absolute cross sections were measured using a dual-source, merged fast-beams apparatus for relative collision energies between ~10 meV to ~10 eV (Hillenbrand et al. 2019). A semi-empirical model was developed incorporating high level quantum mechanical ab initio calculations for the zero-point-energy-corrected potential energy barrier in order to generate thermal rate coefficients for astrochemical models. Based on our studies, we find that these three reactions proceed too slowly at prestellar core temperatures to play a significant role in the deuteration of H $${ + \over 3}$$ isotopologues.

scholarly journals BEAMDB and MOLD—Databases at the Serbian Virtual Observatory for Collisional and Radiative Processes

Atoms ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 11 ◽  
Author(s):  
Bratislav Marinković ◽  
Vladimir Srećković ◽  
Veljko Vujčić ◽  
Stefan Ivanović ◽  
Nebojša Uskoković ◽  
...  
Keyword(s):  
Cross Sections ◽  
Molecular Data ◽  
Molecular Ions ◽  
Progress Report ◽  
Rate Coefficients ◽  
Virtual Observatory ◽  
Radiative Processes ◽  
Recombination Processes ◽  
Molecular Databases ◽  
Rovibrational States

In this contribution we present a progress report on two atomic and molecular databases, BEAMDB and MolD, which are web services at the Serbian virtual observatory (SerVO) and nodes within the Virtual Atomic and Molecular Data Center (VAMDC). The Belgrade Electron/Atom (Molecule) DataBase (BEAMDB) provides collisional data for electron interactions with atoms and molecules. The Photodissociation (MolD) database contains photo-dissociation cross sections for individual rovibrational states of diatomic molecular ions and rate coefficients for the chemi-ionisation/recombination processes. We also present a progress report on the major upgrade of these databases and plans for the future. As an example of how the data from the BEAMDB may be used, a review of electron scattering from methane is described.

scholarly journals Photodestruction of Diatomic Molecular Ions: Laboratory and Astrophysical Application

Molecules ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 151
Author(s):  
Vladimir A. Srećković ◽  
Ljubinko M. Ignjatović ◽  
Milan S. Dimitrijević
Keyword(s):  
Cross Sections ◽  
Alkali Metals ◽  
Molecular State ◽  
Molecular Ions ◽  
Rate Coefficients ◽  
Astrophysical Plasmas ◽  
Stellar Objects ◽  
Laboratory Plasmas ◽  
Rovibrational States ◽  
The Individual

In this work, the processes of photodissociation of some diatomic molecular ions are investigated. The partial photodissociation cross-sections for the individual rovibrational states of the diatomic molecular ions, which involves alkali metals, as well as corresponding data on molecular species and molecular state characterizations, are calculated. Also, the average cross-section and the corresponding spectral absorption rate coefficients for those small molecules are presented in tabulated form as a function of wavelengths and temperatures. The presented results can be of interest for laboratory plasmas as well as for the research of chemistry of different stellar objects with various astrophysical plasmas.

scholarly journals Mol-D a Database and a Web Service within the Serbian Virtual Observatory and the Virtual Atomic and Molecular Data Centre

2016 ◽  
Vol 12 (S325) ◽  
pp. 393-396 ◽  
Author(s):  
Vladimir A. Srećković ◽  
Darko Jevremović ◽  
Veljko Vujčić ◽  
Ljubinko M. Ignjatović ◽  
Nenad Milovanović ◽  
...  
Keyword(s):  
Web Service ◽  
Cross Sections ◽  
Molecular Data ◽  
Molecular Ions ◽  
Stellar Atmospheres ◽  
Rate Coefficients ◽  
Virtual Observatory ◽  
Stage Of Development ◽  
Initial Stage ◽  
Ongoing Work

AbstractIn this contribution we report the current stage of the MOLecular Dissociation (MOL-D) database which is a web service within the Serbian virtual observatory (SerVO) and node within Virtual Atomic and Molecular Data Center (VAMDC). MOL-D is an atomic and molecular (A&M) database devoted to the modelling of stellar atmospheres, laboratory plasmas, industrial plasmas etc. The initial stage of development was done at the end of 2014, when the service for data connected with hydrogen and helium molecular ions was done. In the next stage of the development of MOL-D, we include new cross-sections and rate coefficients for processes which involve species such as XH+, where X is atom of some metal. Data are important for the exploring of the interstellar medium as well as for the early Universe chemistry and for the modeling of stellar and solar atmospheres. In this poster, we present our ongoing work and plans for the future.

scholarly journals Reactive collision of electrons with CO+ in cometary coma

2018 ◽  
Vol 615 ◽  
pp. A53 ◽  
Author(s):  
Y. Moulane ◽  
J. Zs. Mezei ◽  
V. Laporta ◽  
E. Jehin ◽  
Z. Benkhaldoun ◽  
...  
Keyword(s):  
Cross Sections ◽  
Vibrational Excitation ◽  
Dissociative Recombination ◽  
Molecular Data ◽  
Molecular Ions ◽  
Rate Coefficients ◽  
Nuclear Dynamics ◽  
Cometary Coma ◽  
Reactive Collisions ◽  
The Cross

Context. In order to improve our understanding of the kinetics of the cometary coma, theoretical studies of the major reactive collisions in these environments are needed. Deep in the collisional coma, inelastic collisions between thermal electrons and molecular ions result in recombination and vibrational excitation, the rates of these processes being particularly elevated due to the high charged particle densities in the inner region. Aims. This work addresses the dissociative recombination, vibrational excitation, and vibrational de-excitation of electrons with CO+ molecular cations. The aim of this study is to understand the importance of these reactive collisions in producing carbon and oxygen atoms in cometary activity. Methods. The cross-section calculations were based on multichannel quantum defect theory. The molecular data sets, used here to take into account the nuclear dynamics, were based on ab initio R-matrix approach. Results. The cross-sections for the dissociative recombination, vibrational excitation, and vibrational de-excitation processes, for the six lowest vibrational levels of CO+ – relevant for the electronic temperatures observed in comets – are computed, as well as their corresponding Maxwell rate coefficients. Moreover, final state distributions for different dissociation pathways are presented. Conclusions. Among all reactive collisions taking place between low-energy electrons and CO+, the dissociative recombination is the most important process at electronic temperatures characterizing the comets. We have shown that this process can be a major source of O(3P), O(1D), O(1S), C(3P) and C(1D) produced in the cometary coma at small cometocentric distances.

Temperature Dependences of Photodissociation Cross Sections in Krypton Plasma

2020 ◽  
Vol 47 (10) ◽  
pp. 308-312
Author(s):  
K. S. Kislov ◽  
A. A. Narits ◽  
V. S. Lebedev
Keyword(s):  
Cross Sections ◽  
Temperature Dependences

Inelastic scattering of interstellar silyl cyanide (SiH3CN) by helium atoms : cross-sections and rate coefficients for A- and E-SiH3CN

2021 ◽  
Vol 507 (4) ◽  
pp. 5264-5271
Author(s):  
Manel Naouai ◽  
Abdelhak Jrad ◽  
Ayda Badri ◽  
Faouzi Najar
Keyword(s):  
Inelastic Scattering ◽  
Total Energy ◽  
Cross Sections ◽  
Three Dimensional ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Explicitly Correlated ◽  
Correlation Consistent ◽  
Triple Excitation

ABSTRACT Rotational inelastic scattering of silyl cyanide (SiH3CN) molecule with helium (He) atoms is investigated. Three-dimensional potential energy surface (3D-PES) for the SiH3CN–He interacting system is carried out. The ab initio 3D-PES is computed using explicitly correlated coupled cluster approach with single, double, and perturbative triple excitation CCSD(T)-F12a connected to augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. A global minimum at (R = 6.35 bohr; θ = 90○; ϕ = 60○) with a well depth of 52.99 cm−1 is pointed out. Inelastic rotational cross-sections are emphasized for the 22 first rotational levels for total energy up to 500 cm−1 via close coupling (CC) approach in the case of A-SiH3CN and for the 24 first rotational levels for total energy up to 100 cm−1 via CC and from 100 to 500 cm−1 via coupled states (CS) in the case of E-SiH3CN. Rate coefficients are derived for temperature until 80 K for both A- and E-SiH3CN–He systems. Propensity rules are obtained for |ΔJ| = 2 processes with broken parity for A-SiH3CN and for |ΔJ| = 2 processes with |ΔK| = 0 and unbroken parity for E-SiH3CN.

scholarly journals Electron-impact double ionization of the carbon atom

2018 ◽  
Vol 620 ◽  
pp. A188 ◽  
Author(s):  
Valdas Jonauskas
Keyword(s):  
Carbon Atom ◽  
Electron Impact ◽  
Cross Sections ◽  
Double Ionization ◽  
Impact Excitation ◽  
Rate Coefficients ◽  
Electron Impact Excitation ◽  
Ionization Cross ◽  
Ionization Cross Sections ◽  
Good Agreement

Electron-impact single- and double-ionization cross sections and Maxwellian rate coefficients are presented for the carbon atom. Scaling factors are introduced for the electron-impact excitation and ionization cross sections obtained in the distorted wave (DW) approximation. It is shown that the scaled DW cross sections provide good agreement with measurements for the single ionization of the C atom and C1+ ion. The direct double-ionization (DDI) process is studied using a multi-step approach. Ionization–ionization, excitation–ionization–ionization, and ionization–excitation–ionization branches are analyzed. It is demonstrated that the three-step processes contribute ≼40% of the total DDI cross sections for the case where one of the electrons takes all of the excess energy after the first ionization process.

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